Alkaline storage battery

ABSTRACT

An alkaline storage battery includes: [a] a shallow case having an opening and a bottom; [b] a sealing plate covering the opening of the case; [c] a first electrode adjacent to an inner face of the bottom of the case; [d] a second electrode adjacent to an inner face of the sealing plate; [e] a separator interposed between the first electrode and the second electrode; [f] an alkaline electrolyte; and [g] at least one current collector plate selected from the group consisting of (g1) a conductive current collector plate joined to the inner face of the bottom of the case and forming a gas transfer path distributed two-dimensionally between the inner face of the bottom of the case and the first electrode and (g2) a conductive current collector plate joined to the inner face of the sealing plate and forming a gas transfer path distributed two-dimensionally between the inner face of the sealing plate and the second electrode.

TECHNICAL FIELD

The present invention relates to alkaline storage batteries, such asnickel metal-hydride storage batteries, nickel zinc storage batteries,and nickel cadmium storage batteries, and particularly, to flat-typealkaline storage batteries such as a button-type or a coin-type.

BACKGROUND ART

An alkaline storage battery having a flat shape, such as a button shapeor a coin shape, consists of: a shallow case with an opening and abottom; a sealing plate closing the opening of the case; an insulatinggasket interposed between the case and the sealing plate; a positiveelectrode and a negative electrode accommodated in the case; a separatorinterposed between the positive and negative electrodes; and an alkalineelectrolyte. The positive and negative electrodes and the separator,which are porous, retain the electrolyte containing potassium hydroxideand the like. Accordingly, smooth electrochemical reactions becomepossible.

The positive electrode comprises a core material into which nickelhydroxide is filled, and the positive electrode core material is made ofporous sintered nickel, foam metal, or the like. The negative electrodecomprises a core material to which cadmium, zinc, a hydrogen storagealloy, or the like is applied or into which it is filled, and thenegative electrode core material is made of punched metal, foam metal,or the like.

In alkaline storage batteries, at the final stage of charging and uponovercharge, oxygen gas is electrochemically produced from the positiveelectrode, and the oxygen gas is reduced by the negative electrode andreturns to water. In nickel metal-hydride storage batteries, at thefinal stage of charging and upon overcharge, hydrogen is also producedfrom the negative electrode, and the hydrogen gas is chemically absorbedby the negative electrode. If these gases are not promptly consumed, theinternal pressure of the batteries rises, resulting in batteryexpansion. Battery thickness tends to increase particularly in alkalinestorage batteries having a flat shape, such as a button shape or a coinshape.

The produced oxygen gas stays near the inner bottom face of the caseadjacent to the positive electrode or the inner face of the sealingplate and moves the electrolyte, causing a localized distribution of theelectrolyte. As a result, smooth electrochemical reactions are hindered,leading to impaired charging efficiency. In cases where the localizeddistribution of the electrolyte persists even after charging hasfinished, it becomes difficult to obtain a predetermined dischargecapacity, even if discharging is started relatively shortly after thecompletion of charging.

As described above, the speed of gas consumption in alkaline storagebatteries greatly affects battery dimensions andelectrochemical-characteristics.

Therefore, maximizing the speed of gas consumption becomes important.Proposals to facilitate prompt gas consumption include the followings.

Japanese Unexamined Patent Publication No. 2000-507386 proposesproviding a groove on at least one face of a core material of a bipolarelectrode.

Japanese Laid-Open Patent Publication No. 2001-250579 proposes providinga depression on the face of a negative electrode adjacent to the innerface of a sealing plate, and providing a core material portion thatcarries no active material in a positive electrode at the part adjacentto the inner bottom face of a battery case.

In alkaline storage batteries having a flat shape, such as a buttonshape or a coin shape, it is essential to lower the contact resistancebetween the electrode and the inner bottom face of the case or the innerface of the sealing plate. Such batteries tend to have contactresistance greater than that of cylindrical batteries including a woundelectrode plate group, because of the low pressure by which theelectrodes are pressed against the case or the sealing plate. Thisproblem is particularly serious for the positive electrode that usesnickel hydroxide having poor conductivity or the like as the activematerial.

The contact resistance can be reduced by connecting the electrode corematerial with the case or the sealing plate via a current-collectinglead. In this case, however, battery structure becomes complicated,thereby increasing costs. Also, when a gasket is fitted, the positiveand negative electrodes must be positioned correctly such that they areaccommodated inside the gasket. However, the existence of thecurrent-collecting lead makes the positioning of the electrodesdifficult, thereby increasing the incidence of defects and decreasingproduction speed in mass production.

As proposed in Japanese Laid-Open Patent Publication No. 2001-250579,when a core material portion carrying no active material is provided inthe positive electrode at the part adjacent to the inner bottom face ofthe battery case, the contact resistance between the positive electrodeand the battery case can be reduced to a relatively low level, but it isnot low enough. Further, to obtain such a positive electrode, the activematerial needs to be filled from one side of the core material such thatthe active material does not reach the other side. Thus, the fillquantity of the active material varies easily, so that great effort isnecessary for controlling it.

DISCLOSURE OF INVENTION

It is therefore an object of the present invention to suppressdimensional changes caused by the increase in battery internal pressureat the final stage of charging and upon overcharge, and the degradationin electrochemical characteristics due to uneven electrolytedistribution. It is another object of the present invention to reducethe contact resistance between the electrode and the case or the sealingplate. It is still another object of the present invention to provide analkaline storage battery having excellent electrochemicalcharacteristics and small internal resistance at low costs.

That is, the present invention relates to an alkaline storage batteryincluding: [a] a shallow case having an opening and a bottom; [b] asealing plate covering the opening of the case; [c] a first electrodeadjacent to an inner face of the bottom of the case; [d] a secondelectrode adjacent to an inner face of the sealing plate; [e] aseparator interposed between the first electrode and the secondelectrode; [f] an alkaline electrolyte; and [g] at least one currentcollector plate selected from the group consisting of (g1) a conductivecurrent collector plate joined to the inner face of the bottom of thecase and forming a gas transfer path distributed two-dimensionallybetween the inner face of the bottom of the case and the first electrodeand (g2) a conductive current collector plate joined to the inner faceof the sealing plate and forming a gas transfer path distributedtwo-dimensionally between the inner face of the sealing plate and thesecond electrode.

The present invention also pertains to an alkaline storage batteryincluding: [a] a shallow case having an opening and a bottom; [b] asealing plate covering the opening of the dase; [c] a first electrodeadjacent to an inner fade of the bottom of the case; [d] a secondelectrode adjacent to an inner face of the sealing plate; [e] aseparator interposed between the first electrode and the secondelectrode; [f] an alkaline electrolyte; and (g1) at least one spacerjoined to the inner face of the bottom of the case and having at leastone protrusion that forms a gas transfer path distributedtwo-dimensionally between the inner face of the bottom of the case andthe first electrode, and/or (g2) at least one spacer joined to the innerface of the sealing plate and having at least one protrusion that formsa gas transfer path distributed two-dimensionally between the inner faceof the sealing plate and the second electrode.

The present invention is also directed to an alkaline storage batteryincluding: [a] a shallow case having an opening and a bottom; [b] asealing plate covering the opening of the case; [c] a first electrodeadjacent to an inner face of the bottom of the case; [d] a secondelectrode adjacent to an inner face of the sealing plate; [e] aseparator interposed between the first electrode and the secondelectrode; [f] an alkaline electrolyte; and [g] at least one currentcollector plate selected from the group consisting of (g1) a conductivecurrent collector plate joined to the inner face of the bottom of thecase and forming a gap between the inner face of the bottom of the caseand the first electrode and (g2) a conductive current collector platejoined to the inner face of the sealing plate and forming a gap betweenthe inner face of the sealing plate and the second electrode.

The gap between the inner face of the bottom of the case and the firstelectrode or the gap between the inner face of the sealing plate and thesecond electrode may be filled with the electrolyte, but the gap must bea space in which no battery components other than the electrolyte exist.

One of the first electrode and the second electrode is preferably anegative electrode having a core material comprising punched metal.

The present invention is particularly effective when one of the firstelectrode and the second electrode is a negative electrode comprising ahydrogen storage alloy or zinc.

The present invention includes, for example, the following modes:

1(i) An alkaline storage battery including: [a] a shallow case having anopening and a bottom; [b] a sealing plate covering the opening of thecase; [c] a positive electrode adjacent to the inner face of the bottomof the case; [d] a negative electrode adjacent to the inner face of thesealing plate; (e) a separator interposed between the positive electrodeand the negative electrode; [f] an alkaline electrolyte; and [g] atleast one positive electrode current collector plate joined to the innerface of the bottom of the case and forming a gas transfer pathdistributed two-dimensionally between the inner face of the bottom ofthe case and the positive electrode;

-   -   (ii) An alkaline storage battery including: [a] a shallow case        having an opening and a bottom; [b] a sealing plate covering the        opening of the case; [c] a positive electrode adjacent to the        inner face of the bottom of the case; [d] a negative electrode        adjacent to the inner face of the sealing plate; [e] a separator        interposed between the positive electrode and the negative        electrode; [f] an alkaline electrolyte; and [g] at least one        negative electrode current collector plate joined to the inner        face of the sealing plate and forming a gas transfer path        distributed two-dimensionally between the inner face of the        sealing plate and the negative electrode;    -   (iii) An alkaline storage battery including: [a] a shallow case        having an opening and a bottom; [b] a sealing plate covering the        opening of the case; [c] a negative electrode adjacent to the        inner face of the bottom of the case; [d] a positive electrode        adjacent to the inner face of the sealing plate; [e] a separator        interposed between the positive electrode and the negative        electrode; [f] an alkaline electrolyte; and [g] at least one        negative electrode current collector plate joined to the inner        face of the bottom of the case and forming a gas transfer path        distributed two-dimensionally between the inner face of the        bottom of the case and the negative electrode;    -   (iv) An alkaline storage battery including: [a] a shallow case        having an opening and a bottom; [b] a sealing plate covering the        opening of the case; [c] a negative electrode adjacent to the        inner face of the bottom of the case; [d] a positive electrode        adjacent to the inner face of the sealing plate; [e] a separator        interposed between the positive electrode and the negative        electrode; [f] an alkaline electrolyte; and (g2) at least one        positive electrode current collector plate joined to the inner        face of the sealing plate and forming a gas transfer path        distributed two-dimensionally between the inner face of the        sealing plate and the positive electrode;    -   (v) An alkaline storage battery including: [a] a shallow case        having an opening and a bottom; [b] a sealing plate covering the        opening of the case; [c] a positive electrode adjacent to the        inner face of the bottom of the case; [d] a negative electrode        adjacent to the inner face of the sealing plate; [e] a separator        interposed between the positive electrode and the negative        electrode; [f] an alkaline electrolyte; (g1) at least one        positive electrode current collector plate joined to the inner        face of the bottom of the case and forming a gas transfer path        distributed two-dimensionally between the inner face of the        bottom of the case and the positive electrode; and (g2) at least        one negative electrode current collector plate joined to the        inner face of the sealing plate and forming a gas transfer path        distributed two-dimensionally between the inner face of the        sealing-plate and the negative electrode;    -   (vi) An alkaline storage battery including: [a] a shallow case        having an opening and a bottom; [b] a sealing plate covering the        opening of the case; [c] a negative electrode adjacent to the        inner face of the bottom of the case; [d] a positive electrode        adjacent to the inner face of the sealing plate; [e] a separator        interposed between the positive electrode and the negative        electrode; [f] an alkaline electrolyte; (g1) at least one        negative electrode current collector plate joined to the inner        face of the bottom of the case and forming a gas transfer path        distributed two-dimensionally between the inner face of the        bottom of the case and the negative electrode; and (g2) at least        one positive electrode current collector plate joined to the        inner face of the sealing plate and forming a gas transfer path        distributed two-dimensionally between the inner face of the        sealing plate and the positive electrode.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of a coin-shaped sealed batterythat is an example of an alkaline storage battery of the presentinvention.

FIG. 2 is an oblique view of an example of a current collector plateused in an alkaline storage battery of the present invention.

FIG. 3 is an oblique view of another example of a current collectorplate used in an alkaline storage battery of the present invention.

FIG. 4 is an oblique view of still another example of a currentcollector plate used in an alkaline storage battery of the presentinvention.

FIG. 5 is an enlarged photograph of the top face of an example of acurrent collector plate used in an alkaline storage battery of thepresent invention.

FIG. 6 is an enlarged photograph of a section of the conductive currentcollector plate of FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

An alkaline storage battery in accordance with the present inventionincludes: [a] a shallow case having an opening and a bottom; [b] asealing plate covering the opening of the case; [c] a first electrodeadjacent to the inner face of the bottom of the case; [d] a secondelectrode adjacent to the inner face of the sealing plate; [e] aseparator interposed between the first electrode and the secondelectrode; and [f] an alkaline electrolyte.

The shallow case having an opening and a bottom refers to a case havingan opening and a bottom used in batteries having a flat shape, such as abutton shape or a coin shape. The diameter of the opening of the case isusually 1.4 to 70 times the thickness (height) of the case. By “thediameter of the opening” is meant the diameter of a circular opening,the shorter axis of an elliptical or substantially elliptical opening,and the shorter side of a rectangular opening.

The alkaline storage battery in accordance with the present inventionfurther includes (g1) a conductive current collector plate joined to theinner face of the bottom of the case and forming a gas transfer pathdistributed two-dimensionally between the inner face of the bottom ofthe case and the first electrode and/or (g2) a conductive currentcollector plate joined to the inner face of the sealing plate andforming a gas transfer path distributed two-dimensionally between theinner face of the sealing plate and the second electrode.

In this battery, there is a space in which no battery components otherthan the electrolyte exist between the electrode and the inner face ofthe bottom of the case and/or between the electrode and the inner faceof the sealing plate. Therefore, since gas produced from the electrodecan move speedily, oxygen gas produced from the positive electrode atthe final stage of charging and upon overcharge passes through theperiphery of the positive electrode and reaches the negative electrode,where it is reduced and returns to water. This makes it possible toprevent the battery internal pressure from becoming abnormally high.This also makes it possible to prevent the localized distribution of theelectrolyte caused by stagnant oxygen gas or hydrogen gas between theinner face of the bottom of the case and the electrode and/or betweenthe inner face of the sealing plate and the electrode.

To make full use of such advantages, it is preferred to use aplate-shaped electrode that can be arranged in parallel with the innerface of the bottom of the case or the inner face of the sealing plate.

The gas transfer path is preferably distributed in an area of 50 to 100%of the whole inner face of the bottom of the case or the whole innerface of the sealing plate.

Examples of the conductive current collector plate that can be usedinclude a current collector plate that comprises a conductive porousmaterial having pores that communicate with one another (hereinafterreferred to as current collector plate A) and a conductive sheet havinga plurality of protrusions (hereinafter referred to as current collectorplate B). Examples of the conductive porous material having pores thatcommunicate with one another include a foam nickel sheet and expandedmetal. The conductive sheet having a plurality of protrusions may have aplurality of pores. The conductive sheet having a plurality ofprotrusions may be a net having a plurality of protrusions.

Metals such as nickel, stainless, iron, and copper can be used as thematerial of the current collector plate, as well as carbon. Also,nickel-plated iron and the like can be used.

Since the current collector plates A and B are in the form of a plate, asheet or a net, they can be joined to the almost entire inner face ofthe bottom of the case or the almost entire inner face of the sealingplate. Accordingly, the contact resistance between the electrode and thebattery case or between the electrode and the sealing plate can bedrastically reduced. Also, the current collector plates A and B have ashape in which they can be positioned over the almost entire inner faceof the bottom of the case or the almost entire inner face of the sealingplate. Thus, in mounting an electrode on the current collector plate,the position of the electrode can be determined accurately. Accordingly,in mass production, the incidence of defects does not increase, nor doesthe speed of production decrease.

Since the current collector plates A and B are not part of the electrodecore material, there is no need to provide a core material portion inthe positive electrode, as proposed by Japanese Laid-Open PatentPublication No. 2001-250579, that carries no active material at the partadjacent to the inner face of the bottom of the battery case. Therefore,the quantity of the active material filled into the electrode corematerial does not change significantly, nor is great effort necessaryfor controlling the fill quantity.

The apparent thickness of the current collector plate B including theprotrusions is preferably 100 μm or more. If the apparent thickness ofthe current collector plate B becomes less than 100 μm, the gas transferpath is reduced accordingly, impairing the effect of suppressing unevenelectrolyte distribution.

In order to sufficiently ensure the effect of suppressing unevenelectrolyte distribution, it is preferred that the distance between thefirst electrode and the inner face of the bottom of the case or thedistance between the second electrode and the inner face of the sealingplate be 100 μm or more.

The apparent thickness of the current collector plate B including theprotrusions is preferably ⅓ or less of the thickness of the adjacentelectrode. If the apparent thickness of the current collector plate Bexceeds ⅓ of the thickness of the electrode, the energy density of thebattery decreases.

It is preferred that the tip ends of the plurality of protrusions of thecurrent collector plate B be buried in the adjacent electrode. Thisstructure enables a further reduction in the contact resistance betweenthe electrode and the battery case or between the electrode and thesealing plate. In order to effectively reduce the contact resistancebetween the electrode and the battery case or between the electrode andthe sealing plate, it is preferred that the tip ends of the protrusionsof the current collector plate B buried in the electrode have a lengththat is 10% or more of the apparent thickness of the current collectorplate B including the protrusions. As long as the length of the tip endsburied in the electrode is 10% or more of the apparent thickness, thecontact resistance can be reduced to almost the same extent.

A current collector plate that comprises, for example, a metal sheetdeformed by punching from one side or both sides and having a pluralityof pores and burrs formed around the pores (hereinafter referred to ascurrent collector plate C) can be used as the current collector plate B.

The material thickness of the metal sheet used for the current collectorplate C is preferably 10 to 100 μm, and more preferably 20 to 50 μm.When metal sheets are punched from one side or both sides, burrs aresimultaneously formed around the resultant pores in the metal sheets.Examples of the metal sheet include metal foil and metal plates.

The apparent thickness of the current collector plate B including theburrs is preferably equal to or more than twice the material thicknessof the metal sheet. If the apparent thickness of the current collectorplate B is less than twice the material thickness of the metal sheet, itis difficult to provide a sufficient gas transfer path and to bury theburrs sufficiently in the electrode.

There is no limitation with respect to the shape of the pores to beformed in the metal sheet, and circular, triangular or rectangular porescan be formed. Among them, because of the ease of working, circular orrectangular pores are preferable, and circular pores are particularlypreferable. There is also no limitation with regard to the size of thepores, but the area of one pore is preferably 0.02 to 3mm². In the caseof circular pores, the pore radius is preferably 0.08 to 1 mm.

In the current collector plate C, it is preferred that pores closest toeach other be formed by punching from opposite sides and that burrsformed around the pores protrude in mutually opposing directions. Also,it is preferred that the distance between the centers of the poresclosest to each other be 0.3 mm or more and 5 mm or less.

The metal sheet before being deformed by punching may have projectionsand depressions for example in wavelike or zigzag form. The projectionsand depressions can be provided by embossing. When a metal sheet havingprojections and depressions is punched to form a plurality of pores, theapparent thickness of the current collector plate C is the sum of thematerial thickness of the metal sheet, the thickness increased by theprojections and depressions, and the thickness increased by the burrs.

FIG. 1 is a longitudinal sectional view of a coin-shaped alkalinestorage battery in accordance with one embodiment of the presentinvention. This alkaline storage battery includes: a shallow case 2having an opening and a bottom; a sealing plate 1 covering the openingof the case 2; a positive electrode 4 adjacent to the inner face of thebottom of the case 2; a negative electrode 5 adjacent to the inner faceof the sealing plate 1 and comprising a core material of punched metal;a separator 6 interposed between the positive electrode 4 and thenegative electrode 5; and an alkaline electrolyte.

A netlike conductive sheet 7 having a plurality of protrusions 8 isjoined to the inner face of the bottom of the case 2 as the conductivecurrent collector plate. The tip ends of the protrusions 8 are buried inthe adjacent positive electrode 4. The conductive sheet 7 electricallyconnects the case 2 with the positive electrode 4 and forms a gastransfer path 9 distributed two-dimensionally between the inner face ofthe bottom of the case 2 and the positive electrode 4. The joining ofthe conductive sheet 7 and the inner face of the bottom of the case 2 ispreferably performed by welding.

Next, examples of the current collector plate C are illustrated in FIGS.2 to 4.

FIG. 2 is an example of a current collector plate 20 comprising acircular metal sheet. A plurality of rectangular pores 22 are formed ina metal sheet 21 by punching from both sides. Around each of the pores22 are four pointed burrs 23 a or 23 b.

FIG. 3 is another example of a current collector plate 30 comprising acircular metal sheet. A plurality of triangular pores 32 are formed in ametal sheet 31 by punching from both sides. Around each of the pores 32is one pointed burr 33 a or 33 b.

FIG. 4 is still another example of a current collector plate 40comprising a circular metal sheet. A plurality of circular pores 42 areformed in a metal sheet 41 by punching from both sides. Around each ofthe pores 42 are a plurality of pointed burrs 43 a or 43b.

The tip ends of the burrs 23 a, 33 a, and 43 a protruding in onedirection can be buried in an electrode. The burrs 23 b, 33 b, and 43 bprotruding in the opposite direction are welded to the inner face of thebottom of the battery case or the inner face of the sealing plate. Fromthe viewpoint of sufficiently ensuring the gas transfer path, it ispreferred to form burrs such that the burrs alternately protrude inopposite directions, as shown in FIGS. 2 to 4.

The present invention is particularly effective when the negativeelectrode comprises a hydrogen storage alloy or zinc. The negativeelectrode comprising a hydrogen storage alloy produces hydrogen gas,while the negative electrode comprising zinc exhibits slow oxygen gasabsorption. It is therefore preferred to form a gas transfer path on thenegative electrode side as well. The present invention is also effectivewhen the negative electrode comprises cadmium.

The present invention is particularly effective when the negativeelectrode core material comprises punched metal. The reason is asfollows. Since such negative electrodes are generally highly dense,electrolyte exhaustion tends to occur therein. However, if the gastransfer path is adjacent to the negative electrode, uneven electrolytedistribution is corrected, so that electrolyte exhaustion is unlikely tooccur. The negative electrode comprising the core material of punchedmetal is inexpensive and has little variation in quality, and hence, issuited for mass production.

In the following, the present invention is specifically described by wayof examples. These examples, however, are not to be construed aslimiting in any way the present invention.

EXAMPLE 1

(i) Preparation of Positive Electrode

Nickel hydroxide containing Co and Zn was used as a positive electrodeactive material. 100 parts by weight of this active material was mixedwith 10 parts by weight of cobalt hydroxide and a proper amount ofwater. The resultant mixture was filled into the pores of a 1.2 mm thickfoam nickel substrate. This was dried, rolled, and cut into a roundshape with a diameter of 9.2 mm, to provide a positive electrode. Thethickness of the resultant positive electrode was about 0.78 mm. Thetheoretical capacity of the positive electrode (the capacity obtainedwhen one-electron reaction of all the nickel in the nickel hydroxideoccurs) was 30 mAh.

(ii) Preparation of Negative Electrode

A hydrogen storage alloy of the known AB₅ type(MMNi_(3.55)Co_(0.75)Al_(0.3)Mn_(0.4): Mm represents misch metal) wasused as a negative electrode material. This alloy was pulverized into amean grain size of 35 μm and was then treated with an aqueous KOHsolution. 100 parts by weight of the treated alloy powder was mixed with0.7 part by weight of a binder (styrene-butadiene rubber), 0.15 part byweight of carboxymethyl cellulose, and a proper amount of water. Theresultant mixture was applied onto a 60 μm thick punched metal substrate(perforated metal plate) plated with nickel. This was dried, rolled, andcut into a round shape with a diameter of 9.2 mm, to provide a negativeelectrode. The thickness of the resultant negative electrode was about0.47 mm. The capacity of the negative electrode was made larger thanthat of the positive electrode, and the battery capacity was determinedby the capacity of the positive electrode.

(iii) Preparation of Current Collector Plate

A 30 μm thick nickel sheet was passed between upper and lower rollswhose surfaces had needle-like, quadrangular-pyramid-shaped protrusions.The needle-like, quadrangular-pyramid-shaped protrusions alternatelypierced the nickel sheet in opposite directions, thereby formingrectangular pores and burrs at the same time. The resultant nickel platehaving a plurality of pores and burrs formed around the pores was cutinto a round shape with a diameter of about 9 mm, to obtain a currentcollector plate as illustrated in FIG. 2. The apparent thickness of theresultant current collector plate including the burrs was about 350 μm,and the center-to-center distance between the pores closest to eachother was 0.7 mm, and the area of one pore was about 0.04 mm².

(iv) Assembly of Battery

A polypropylene non-woven fabric subjected to a hydrophilic treatmentwas used as a separator, and an aqueous solution dissolving about 7mol/L potassium hydroxide and about 1 mol/L lithium hydroxide was usedas an electrolyte.

The negative electrode was joined to the inner face of a sealing plate,and the separator was mounted on the negative electrode. A gasket wasthen fitted to the circumference of the sealing plate. The electrolytewas injected into the sealing plate, and the positive electrode wasmounted on the separator. Thereafter, a case having an opening and abottom, whose inner face (a round shape with a diameter of about 12 mm)had been welded to the current collector plate, was mounted so as tocover the positive electrode. The opening edge of the case was crimpedonto the gasket fitted to the circumference of the sealing plate, toseal the case. As a result, a coin-shaped nickel metal-hydride storagebattery A with a diameter of about 12.5 mm was completed. The height ofthe battery A was about 2.1 mm.

(v) Examination and Evaluation of Battery

[Examination]

Six batteries A were produced. Of them, three batteries A were cut, andtheir sectional structures were observed. It was found that the apparentthickness of the current collector plates including the burrs was about250 μm. However, before the production of the batteries A, the apparentthickness of the current collector plates was about 350 μm. Upon thesealing of the batteries, the current collector plates were pressed bythe case and the positive electrode, so that the ends of the burrs weredeformed. The tip ends of the burrs of the current collector plates wereburied in the positive electrode to a depth of about 50 μm. It wasobserved that there was a gap in which the core material, the activematerial and the like did not exist between the positive electrode andthe case.

[Evaluation]

The remaining three batteries A were evaluated for their electrochemicalcharacteristics.

Each battery was charged at 3 mA at an ambient temperature of 20° C. for15 hours, and after an interval of 1 hour, it was discharged at 6 mAdown to a cut-off voltage of 1 V. This charge/discharge cycle wasrepeated 5 times. The average discharge capacity (C_(6mA)) at the 5thcycle was 28 mAh, i.e., the positive electrode utilization rate(U_(6mA-R)) was 93%.

The increase (Δh_(5th)) in battery height after 5 charge/dischargecycles was about 50 μm, compared to the height immediately after thebattery production.

The internal impedance (I_(5th)) after 5 charge/discharge cycles wasabout 1 Ω at 1 kHz.

Then, each of the batteries A was charged at 3 mA at an ambienttemperature of 20° C. for 15 hours, and after an interval of 1 hour, itwas discharged at 30 mA down to a cut-off voltage of 1 V. At this time,the average discharge capacity (C_(30mA)) was 23 mAh.

Subsequently, each battery was charged at 30 mA at an ambienttemperature of 20° C. for 1.2 hours and discharged at 30 mA down to acut-off voltage of 1 V. This charge/discharge cycle was repeated 300times. The average discharge capacity (C_(20mA-300th)) at the 300thcycle was 20 mAh.

The battery height after 300 charge/discharge cycles remained almostunchanged from before the cycle life test.

The internal impedance (I_(300th)) after 300 charge/discharge cycles wasabout 1.5 Ω at 1 kHz.

In this example, only one current collector plate was used. However,there is no limitation with respect to the number of current collectorplates, and the use of a plurality of current collector plates does notimpair the effects of the present invention.

COMPARATIVE EXAMPLE 1

Coin-shaped nickel metal-hydride storage batteries B were produced inthe same manner as in Example 1, except that the current collectorplates used in Example 1 were not used. The height of the batteries Bwas about 1.9 mm.

The batteries B were evaluated for their electrochemical characteristicsin the same manner as in Example 1.

The average discharge capacity (C_(6mA)) of the batteries B at the 5thcycle upon 6 mA discharge was 21 mAh, i.e., the positive electrodeutilization rate (U_(6mA-R)) was 70%.

The increase (Δh_(5th)) in battery height after 5 charge/dischargecycles was about 150 μm, compared to the height immediately after thebattery production.

The internal impedance (I_(5th)) after 5 charge/discharge cycles wasabout 2 Ω at 1 kHz.

Then, each of the batteries B was charged at 3 mA at an ambienttemperature of 20° C. for 15 hours, and after an interval of 1 hour, itwas discharged at 30 mA down to a cut-off voltage of 1 V. At this time,the average discharge capacity (C_(30mA)) was 13 mAh.

The above results indicate that the discharge capacity, high-ratedischarge characteristics and internal impedance of the batteries A arefar superior to those of the batteries B.

Thereafter, each battery was charged at 30 mA at an ambient temperatureof 20° C. for 1.2 hours and discharged at 30 mA down to a cut-offvoltage of 1 V. This charge/discharge cycle was repeated 300 times. As aresult, the average discharge capacity (C_(20mA-300th)) at the 300thcycle was 5 mAh.

After 300 charge/discharge cycles, the battery height increased by about200 μm, in comparison with before the cycle life test.

The internal impedance (I_(300th)) after 300 charge/discharge cycles wasabout 5 Ω at 1 kHz.

The above results show that the cycle life characteristics of thebatteries A are far superior to those of the batteries B.

EXAMPLE 2

Coin-shaped nickel metal-hydride storage batteries C-1 and C-2 wereproduced in the same manner as in Example 1, except that the ratio(D_(R)) of the length of the burr tip ends buried in the positiveelectrode to the apparent thickness of the current collector plateincluding burrs was varied by varying the pressure applied to thebattery upon sealing. They were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge, average discharge capacity(C_(30mA)) upon 30 mA discharge, and internal impedance (I_(5th)) after5 charge/discharge cycles. The results are shown in Table 1. TABLE 1Battery D_(R)(%) I_(5th)(Ω) C_(6mA)(mAh) C_(30mA)(mAh) C-1 0 2 25 15 C-210 1 28 23 A 20 1 28 23

Table 1 indicates that good results can be obtained when the ratio ofthe length of the burr tip ends buried in the positive electrode to theapparent thickness of the current collector plate including burrs is 10%or more.

EXAMPLE 3

Coin-shaped nickel metal-hydride storage batteries D-1, D-2, and D-3were produced in the same manner as in Example 1, except that thedistance (D_(P-C)) between the inner bottom face of the case and thepositive electrode was varied. In this example, in order to vary thedistance between the inner bottom face of the case and the positiveelectrode, the dimensions of burrs formed on a 30 μm thick nickel platewere varied in producing current collector plates. The dimensions ofburrs were controlled by varying the dimensions of needle-like,quadrangular-pyramid-shaped protrusions of upper and lower rolls. Thebatteries D-1 to D-3 were evaluated for their average discharge capacity(C_(6mA)) upon 6 mA discharge, average discharge capacity (C_(30mA))upon 30 mA discharge, internal impedance (I_(5th)) after 5charge/discharge cycles, and the increase in battery height (Δh_(5th)),in the same manner as in Example 1. The results are shown in Table 2.TABLE 2 Battery D_(P-C)(μm) I_(5th)(Ω) C_(6mA)(mAh) C_(30mA)(mAh)Δh_(5th) D-1 50 2 22 14 120 D-2 100 1.2 26 19 80 D-3 150 1 26 21 60 A200 1 28 23 50

As shown in Table 2, when the distance between the inner bottom face ofthe case and the positive electrode is less than 100 μm, the dischargecapacity tended to decrease markedly, and battery expansion, i.e., theincrease in battery height, tended to increase. These results show thatthe distance between the inner bottom face of the case and the positiveelectrode is desirably 100 μm or more in order to produce full effectsof the present invention.

To make the distance between the inner bottom face of the case and thepositive electrode 100 μm or more, it is necessary to use a currentcollector plate whose apparent thickness including burrs is 100 μm ormore. However, if the apparent thickness of the current collector plateis too thick, the space inside the battery is wasted, so that thebattery capacity decreases, resulting in a reduction in energy density.From the viewpoint of energy density, setting the apparent thickness ofthe current collector plate to ⅓ or less of the thickness of theadjacent electrode (the positive electrode in this example) waspreferable.

EXAMPLE 4

Coin-shaped nickel metal-hydride storage batteries E-1 and E-2 wereproduced in the same manner as in Example 1, except that a stainlesssteel plate or a nickel-plated steel plate was used as the material ofthe current collector plate in place of the nickel plate. They wereevaluated for their average discharge capacity (C_(6mA)) upon 6 mAdischarge, average discharge capacity (C_(30mA)) upon 30 mA discharge,and internal impedance (I_(5th)) after 5 charge/discharge cycles. Theresults are shown in Table 3. TABLE 3 Current collector Battery plateD_(R)(%) I_(5th)(Ω) C_(6mA)(mAh) C_(30mA)(mAh) E-1 Stainless 10 1 28 23steel E-2 Nickel-plated 10 1 28 23 steel A Nickel 10 1 28 23

The results of Table 3 indicate that the use of a current collectorplate made of any of those materials produces the effects of improvingthe current-collecting characteristics between the case and theelectrode and of facilitating the gas transfer, thereby resulting in abattery having excellent characteristics.

EXAMPLE 5

Coin-shaped nickel metal-hydride storage batteries F-1, F-2, F-3 and F-4were produced in the same manner as in Example 1, except that theapparent thickness of the current collector plates was varied. In thisexample, in order to vary the apparent thickness of the currentcollector plates, the dimensions of burrs formed on a 30 μm thick nickelplate were varied in producing current collector plates. The dimensionsof burrs were controlled by varying the dimensions of needle-like,quadrangular-pyramid-shaped protrusions of upper and lower rolls.

Also, coin-shaped nickel metal-hydride storage batteries F-5 wereproduced in the same manner as in Example 1, except for the use of acurrent collector plate produced by punching a nickel plate from onlyone side. The shapes of the burrs and the pores of the current collectorplate of the batteries F-5 were made the same as those of Example 1.

Further, coin-shaped nickel metal-hydride storage batteries F-6 wereproduced in the same manner as in Example 1, except for the use of acurrent collector plate produced by punching a corrugated nickel plate(the difference in height between the ridges and grooves is 200 μm) fromboth sides. The shapes of the burrs and the pores of the currentcollector plate of the batteries F-6 were made the same as those ofExample 1.

FIG. 5 shows an enlarged photograph of the top face of a currentcollector plate 50 used in the battery F-6. Also, FIG. 6 shows anenlarged photograph of a section of the current collector plate 50.

In FIG. 5, burrs 53 are formed around a pore A 51, which is-made byupward punching with respect to the paper sheet, and a pore B 52, whichis made by downward punching with respect to the paper sheet, as shownin FIG. 6. The interval between the pores A 51 and the interval betweenthe pores B 52 are both about 0.7 mm.

Also, coin-shaped nickel metal-hydride storage batteries F-7 wereproduced in the same manner as in Example 1, except for the use of acurrent collector plate made of foam nickel (thickness: 250 μm;porosity: 98% by volume).

Further, coin-shaped nickel metal-hydride storage batteries F-8 wereproduced in the same manner as in Example 1, except for the use of acurrent collector plate comprising nickel expanded metal (apparentthickness: 250 μm).

The batteries F-1 to F-8 were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge and average discharge capacity(C_(30mA)) upon 30 mA discharge, in the same manner as in Example 1. Theresults are shown in Table 4. TABLE 4 Apparent Current thicknesscollector Punching Battery (μm) plate Corrugation direction C_(6mA)(mAh)C_(30mA)(mAh) F-1 50 Punched No Both 26 20 plate sides F-2 100 PunchedNo Both 27 22 plate sides F-3 150 Punched No Both 27 22 plate sides F-4200 Punched No Both 28 23 plate sides F-5 250 Punched No One side 28 21plate F-6 250 Punched Yes Both 30 25 plate sides F-7 250 Foam No — 27 22nickel F-8 250 Expanded No — 26 20 metal A 250 Punched No Both 28 23plate sides

As shown in Table 4, the batteries F-1, in which the apparent thicknessof the current collector plate is less than twice the material thickness(30 μm) of the nickel plate, had slightly decreased capacities. Thisindicates that the apparent thickness of the current collector plate ispreferably equal to or more than twice the material thickness of themetal sheet before the working. Also, the batteries F-6, in which thenickel plate is corrugated, produced particularly good results. Thebatteries F-5, which include the current collector plate produced bypunching the nickel plate from only one side, also produced goodresults. Further, the batteries F-7 and F-8, which include the currentcollector plates of foam nickel and expanded metal, also produced goodresults.

EXAMPLE 6

Coin-shaped nickel metal-hydride storage batteries G-1 and G-2 wereproduced in the same manner as in Example 1, except that the shape ofpores made in a nickel plate was varied. In this example, currentcollector plates as illustrated in FIGS. 3 and 4 were produced byvarying the shape of the pores, using rolls whose surfaces hadneedle-like, triangular-pyramid-shaped or cone-shaped protrusions,instead of the rolls whose surfaces had needle-like,quadrangular-pyramid-shaped protrusions. In both of the currentcollector plates, the center-to-center distance between the poresclosest to each other was 0.7 mm, and the area of one pore was about0.04 mm².

The batteries G-1 and G-2 were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge and average discharge capacity(C_(30mA)) upon 30 mA discharge, in the same manner as in Example 1. Theresults are shown in Table 5. TABLE 5 Punching Battery Pore shapedirection C_(6mA)(mAh) C_(30mA)(mAh) G-1 Circular Both sides 28 23 G-2Triangular Both sides 27 22 A Rectangular Both sides 28 23

All the batteries produced good results and exerted the effects of thepresent invention. The shape of the pores needs not to be the same, andgood results will also be obtained even in the presence of pores havingdifferent shapes.

EXAMPLE 7

Coin-shaped alkaline storage batteries H-1 and H-2 were produced in thesame manner as in Example 1, except for the use of a cadmium compound ora zinc compound as the negative electrode material. In the case of usinga zinc compound as the negative electrode material, a negative electrodecore material made of copper was used, and a polypropylene micro-porousfilm subjected to a hydrophilic treatment was used as the separator. Thebatteries H-1 and H-2 were evaluated for their positive electrodeutilization rate (U_(6mA-R)) upon 6 mA discharge, positive electrodeutilization rate (U_(30mA-R)) upon 30 mA discharge, and internalimpedance (I_(5th)) after 5 charge/discharge cycles, in the same manneras in Example 1. The results are shown in Table. 6. TABLE 6 Negativeelectrode Battery material I_(5th)(Ω) U_(6mA-R) U_(30mA-R) H-1 Cadmium 193 79 H-2 Zinc 1 93 75 A Hydrogen 1 93 77 storage alloy

All the batteries produced excellent results, and the effects of thepresent invention were also exerted when the alkaline storage batterywas the nickel cadmium storage battery or the nickel zinc storagebattery.

EXAMPLE 8

Next, an explanation is given of the case of interposing a currentcollector plate between the inner face of the sealing plate and thenegative electrode.

(i) Preparation of Current Collector Plate

A current collector plate was produced in almost the same manner as inExample 1. Specifically, a 30 μm thick nickel sheet was passed betweenupper and lower rolls whose surfaces had needle-like,quadrangular-pyramid-shaped protrusions. The needle-like,quadrangular-pyramid-shaped protrusions alternately pierced the nickelsheet in opposite directions, thereby forming rectangular pores andburrs at the same time. The resultant nickel plate having a plurality ofpores and burrs formed around the pores was cut into a round shape witha diameter of about 9 mm, to obtain a current collector plate asillustrated in FIG. 2. The apparent thickness of the resultant currentcollector plate including the burrs was about 250 μm, and thecenter-to-center distance between the pores closest to each other was0.7 mm, and the area of one pore was about 0.04 mm².

(ii) Assembly of Battery

The current collector plate was placed on the inner face (a round shapewith a diameter of about 9 mm) of a sealing plate, and the sealing plateand the current collector plate were welded together. Subsequently, anegative electrode was mounted on the current collector plate, and aseparator was mounted thereon. A gasket was then fitted to thecircumference of the sealing plate. Thereafter, an electrolyte wasinjected into the sealing plate, and a positive electrode was mounted onthe separator. Thereafter, a case having an opening and a bottom wasmounted so as to cover the positive electrode, and the opening edge ofthe case was crimped onto the gasket fitted to the circumference of thesealing plate, to seal the case. As a result, a coin-shaped nickelmetal-hydride storage battery J with a diameter of about 12.5 mm wascompleted. The height of the battery J was about 2. 0 mm.

(v) Examination and Evaluation of Battery

[Examination]

Six batteries J were produced. Of them, three batteries J were cut, andtheir sectional structures were observed. It was found that the apparentthickness of the current collector plates including burrs was about 150μm. However, before the production of the batteries J, the apparentthickness of the current collector plates was about 250 μm. Upon thesealing of the batteries, the current collector plates were pressed bythe sealing plate and the negative electrode, so that the tip ends ofthe burrs were deformed. The tip ends of the burrs of the currentcollector plates were buried in the negative electrode to a depth ofabout 30 μm. It was observed that there was a gap in which the corematerial, the hydrogen storage alloy and the like did not exist betweenthe negative electrode and the sealing plate.

[Evaluation]

The remaining three batteries J were evaluated for their electrochemicalcharacteristics.

Each battery was charged at 3 mA at an ambient temperature of 20° C. for15 hours, and after an interval of 1 hour, it was discharged at 6 mAdown to a cut-off voltage of 1 V. This charge/discharge cycle wasrepeated 5 times. The average discharge capacity (C_(6mA)) at the 5thcycle was 27 mAh, i.e., the positive electrode utilization rate(U_(6mA-R)) was 90%.

The increase (Δh_(5th)) in battery height after 5 charge/dischargecycles was about 50 μm, compared to the height immediately after thebattery production.

The internal impedance (I_(5th)) after 5 charge/discharge cycles wasabout 1 Ω at 1 kHz.

Then, each of the batteries J was charged at 3 mA at an ambienttemperature of 20° C. for 15 hours, and after an interval of 1 hour, itwas discharged at 30 mA down to a cut-off voltage of 1 V. At this time,the average discharge capacity (C_(30mA)) was 22 mAh.

In this example, only one current collector plate was used. However,there is no limitation with respect to the number of current collectorplates, and the use of a plurality of current collector plates does notimpair the effects of the present invention.

EXAMPLE 9

Coin-shaped nickel metal-hydride storage batteries K-1 and K-2 wereproduced in the same manner as in Example 8, except that the ratio(D_(R)) of the length of the burr tip ends buried in the negativeelectrode to the apparent thickness of the current collector plateincluding burrs was varied by varying the pressure applied to thebattery upon sealing. They were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge, average discharge capacity(C_(30mA)) upon 30 mA discharge, and internal impedance (I_(5th)) after5 charge/discharge cycles. The results are shown in Table 7. TABLE 7Battery D_(R)(%) I_(5th)(Ω) C_(6mA)(mAh) C_(30mA)(mAh) K-1 0 2 24 24 K-210 1 27 22 J 20 1 27 22

Table 7 indicates that good results can be-obtained when the ratio ofthe length of the burr tip ends buried in the negative electrode to theapparent thickness of the current collector plate including burrs is 10%or more.

EXAMPLE 10

Coin-shaped nickel metal-hydride storage batteries L-1, L-2, and L-3were produced in the same manner as in Example 8, except that thedistance (D_(N-C)) between the inner face of the sealing plate and thenegative electrode was varied. In this example, in order to vary thedistance between the inner face of the sealing plate and the negativeelectrode, the dimensions of burrs formed on a 30 μm thick nickel platewere varied in producing current collector plates. The dimensions ofburrs were controlled by varying the dimensions of needle-like,quadrangular-pyramid-shaped protrusions of upper and lower rolls. Thebatteries L-1 to L-3 were evaluated for their average discharge capacity(C_(6mA)) upon 6 mA discharge, average discharge capacity (C_(30mA))upon 30 mA discharge, internal impedance (I_(5th)) after 5charge/discharge cycles, and the increase in battery height (Δh_(5th)),in the same manner as in Example 8. The results are shown in Table 8.TABLE 8 Battery D_(N-C)(μm) I_(5th)(Ω) C_(6mA)(mAh) C_(30mA)(mAh)Δh_(5th) L-1 50 2 23 15 150 L-2 70 1.5 25 18 130 L-3 100 1 27 22 70 J120 1 27 22 50

As shown in Table 8, when the distance between the inner face of thesealing plate and the negative electrode is less than 100 μm, thedischarge capacity tended to decrease markedly, and battery expansion,i.e., the increase in battery height, tended to increase. These resultsshow that the distance between the inner face of the sealing plate andthe negative electrode is desirably 100 μm or more in order to producefull effects of the present invention.

To make the distance between the inner face of the sealing plate and thenegative electrode 100 μm or more, it is necessary to use a currentcollector plate whose apparent thickness including burrs is 100 μm ormore. However, if the apparent thickness of the current collector plateis too thick, the space inside the battery is wasted, so that thebattery capacity decreases, resulting in a reduction in energy density.From the viewpoint of energy density, setting the apparent thickness ofthe current collector plate to ⅓ or less of the thickness of theadjacent electrode (the negative electrode in this example) waspreferable.

EXAMPLE 11

Coin-shaped nickel metal-hydride storage batteries M-1 to M-4 wereproduced in the same manner as in Example 8, except that a stainlesssteel plate, a nickel-plated steel plate, a steel plate, or a copperplate was used in place of the nickel plate as the material of thecurrent collector plate. They were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge, average discharge capacity(C_(30mA)) upon 30 mA discharge, and internal impedance (I_(5th)) after5 charge/discharge cycles. The results are shown in Table 9. TABLE 9Current collector Battery plate D_(R)(%) I_(5th)(Ω) C_(6mA)(mAh)C_(30mA)(mAh) M-1 Stainless 10 1 27 22 steel M-2 Nickel- 10 1 27 22plated steel M-3 Steel 10 1 26 21 M-4 Copper 10 1 27 22 J Nickel 10 1 2722

The results of Table 9 indicate that the use of a current collectorplate made of any of those materials produces the effects of improvingthe current-collecting characteristics between the sealing plate and theelectrode and of facilitating the gas transfer, thereby resulting in abattery having excellent characteristics.

EXAMPLE 12

Coin-shaped nickel metal-hydride storage batteries N-1, N-2, and N-3were produced in the same manner as in Example 8, except that theapparent thickness of the current collector plates was varied. In thisexample, in order to vary the apparent thickness of the currentcollector plates, the dimensions of burrs formed on a 30 μm thick nickelplate were varied in producing current collector plates. The dimensionsof burrs were controlled by varying the dimensions of needle-like,quadrangular-pyramid-shaped protrusions of upper and lower rolls.

Also, coin-shaped nickel metal-hydride storage batteries N-4 wereproduced in the same manner as in Example 8, except for the use of acurrent collector plate produced by punching a nickel plate from onlyone side. The shapes of the burrs and the pores of the current collectorplate of the batteries N-4 were made the same as those of Example 8.

Further, coin-shaped nickel metal-hydride storage batteries N-5 wereproduced in the same manner as in Example 8, except for the use of acurrent collector plate produced by punching a corrugated nickel plate(the difference in height between the ridges and grooves is 100 μm) fromboth sides. The shapes of the burrs and the pores of the currentcollector plate of the batteries N-5 were made the same as those ofExample 8.

Also, coin-shaped nickel batteries N-6 were produced in the same manneras in Example 8, except for the use of a current collector plate made offoam nickel (thickness: 150 μm; porosity: 98% by volume).

Further, coin-shaped nickel metal-hydride storage batteries N-7 wereproduced in the same manner as in Example 8, except for the use of acurrent collector plate comprising nickel expanded metal (apparentthickness: 150 μm).

The batteries N-1 to N-7 were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge and average discharge capacity(C_(30mA)) upon 30 mA discharge, in the same manner as in Example 8. Theresults are shown in Table 10. TABLE 10 Apparent Current thicknesscollector Punching Battery (μm) plate Corrugation direction C_(6mA)(mAh)C_(30mA)(mAh) N-1 50 Punched No Both 25 19 plate sides N-2 70 Punched NoBoth 26 21 plate sides N-3 100 Punched No Both 26 21 plate sides N-4 150Punched No One side 27 20 plate N-5 150 Punched Yes Both 29 24 platesides N-6 150 Foam No — 26 21 nickel N-7 150 Expanded No — 25 19 metal J150 Punched No Both 27 22 plate sides

As shown in Table 10, the batteries N-1, in which the apparent thicknessof the current collector plate is less than twice the material thickness(30 μm) of the nickel plate, had slightly decreased capacities. Thisindicates that the apparent thickness of the current collector plate ispreferably equal to or more than twice the material thickness of themetal sheet before the working. Also, the batteries N-5, in which thenickel plate is corrugated, produced particularly good results. Thebatteries N-4, which include the current collector plate produced bypunching the nickel plate from only one side, also produced goodresults. Further, the batteries N-6 and N-7, which include the currentcollector plates of foam nickel and expanded metal, also produced goodresults.

EXAMPLE 13

Coin-shaped nickel metal-hydride storage batteries O-1 and O-2 wereproduced in the same manner as in Example 8, except that the shape ofpores made in a nickel plate was varied. In this example, currentcollector plates as illustrated in FIGS. 3 and 4 were produced byvarying the shape of the pores, using rolls whose surfaces hadneedle-like, triangular-pyramid-shaped or cone-shaped protrusions,instead of the rolls whose surfaces had needle-like,quadrangular-pyramid-shaped protrusions. In both of the currentcollector plates, the center-to-center distance between the poresclosest to each other was 0.7 mm, and the area of one pore was about0.04 mm².

The batteries O-1 and O-2 were evaluated for their average dischargecapacity (C_(6mA)) upon 6 mA discharge and average discharge capacity(C_(30mA)) upon 30 mA discharge, in the same manner as in Example 8. Theresults are shown in Table 11. TABLE 11 Punching Battery Pore shapedirection C_(6mA)(mAh) C_(30mA)(mAh) O-1 Circular Both sides 27 22 O-2Triangular Both sides 26 21 J Rectangular Both sides 27 22

All the batteries produced good results and exerted the effects of thepresent invention. The shape of the pores needs not to be the same, andgood results will also be obtained even in the presence of pores havingdifferent shapes.

EXAMPLE 14

Coin-shaped alkaline storage batteries P-1 and P-2 were produced in thesame manner as in Example 8, except for the use of a cadmium compound ora zinc compound as the negative electrode material. In the case of usinga zinc compound as the negative electrode material, a negative electrodecore material made of copper was used, and a polypropylene micro-porousfilm subjected to a hydrophilic treatment was used as the separator. Thebatteries P-1 and P-2 were evaluated for their positive electrodeutilization rate (U_(6mA-R)) upon 6 mA discharge, positive electrodeutilization rate (U_(30mA-R)) upon 30 mA discharge, and internalimpedance (I_(5th)) after 5 charge/discharge cycles, in the same manneras in Example 8. The results are shown in Table 12. TABLE 12 Negativeelectrode Battery material I_(5th)(Ω) U_(6mA-R) U_(30mA-R) P-1 Cadmium 190 75 P-2 Zinc 1 90 71 J Hydrogen 1 90 73 storage alloy

All the batteries produced excellent results, and the effects of thepresent invention were also produced-when the alkaline storage batterywas the nickel cadmium storage battery or the nickel zinc storagebattery.

EXAMPLE 15

Batteries Q were produced in the same manner as in Example 1, exceptthat the positions of the positive electrode and the negative electrodewere reversed and a current collector plate was welded to the inner faceof the sealing plate. The current collector plate used in this examplewas the same as that in Example 1.

The current collector plate was placed on the inner face (a round shapewith a diameter of about 9 mm) of a sealing plate, and the sealing plateand the current collector plate were welded together. Subsequently, apositive electrode was mounted on the current collector plate, and aseparator was mounted thereon. A gasket was then fitted to thecircumference of the sealing plate. Thereafter, an electrolyte wasinjected into the sealing plate, and a negative electrode was mounted onthe separator. Thereafter, a case having an opening and a bottom wasmounted so as to cover the negative electrode, and the opening edge ofthe case was crimped onto the gasket fitted to the circumference of thesealing plate, to seal the case. As a result, a coin-shaped nickelmetal-hydride storage battery Q with a diameter of about 12.5 mm wascompleted. The height of the battery Q was about 2.1 mm.

The batteries Q were evaluated in the same manner as the batteries A. Asa result, it was found that the internal impedance was 1 Ω the positiveelectrode utilization rate at a discharge current of 6 mA was 93%, andthe discharge capacity at a discharge current of 30 mA was 23 mAh. Theseresults show that the effects of the present invention are exertedwithout depending on the arrangement of the positive electrode and thenegative electrode.

EXAMPLE 16

Batteries R were produced in the same manner as in as in Example 1,except that a current collector plate was also interposed between theinner face of the sealing plate and the negative electrode in the samemanner as in Example 8. In this example, a current collector plate thatwas the same as that of Example 8 was placed on the inner face (a roundshape with a diameter of about 9 mm) of the sealing plate, and thesealing plate and the current collector plate were welded together.Subsequently, a negative electrode was mounted on the current collectorplate, and a separator was mounted thereon. A gasket was then fitted tothe circumference of the sealing plate. Thereafter, an electrolyte wasinjected into the sealing plate, and a positive electrode was mounted onthe separator. Thereafter, a case having an opening and a bottom, whoseinner face (a round shape with a diameter of about 12 mm) had beenwelded to another current collector plate, was mounted so as to coverthe positive electrode, and the opening edge of the case was crimpedonto the gasket fitted to the circumference of the sealing plate, toseal the case. As a result, a coin-shaped nickel metal-hydride storagebattery R with a diameter of about 12.5 mm was completed. The height ofthe battery R was about 2.25 mm.

The batteries R were evaluated in the same manner as the batteries A. Asa result, it was found that the internal impedance was about 0.9 Ω, thepositive electrode utilization rate at a discharge current of 6 mA was95%, and the discharge capacity at a discharge current of 30 mA was 25mAh. These results show that the provision of a current collector platebetween the positive electrode and the inner bottom face of the batterycase and between the negative electrode and the inner face of thesealing plate results in a battery having characteristics superior tothose of the batteries of Example 1 and Example 8.

EXAMPLE 17

Batteries S were produced in the same manner as in Example 15, exceptthat a current collector plate was also interposed between the negativeelectrode and the inner bottom face of the battery case. The currentcollector plate interposed between the negative electrode and the innerbottom face of the battery case was the same as that used in Example 8.

First, a current collector plate which was the same as that of Example 1was placed on the inner face (a round shape with a diameter of about 9mm) of a sealing plate, and the sealing plate and the current collectorplate were welded together. Subsequently, a positive electrode wasmounted on the current collector plate, and a separator was mountedthereon. A gasket was then fitted to the circumference of the sealingplate. Thereafter, an electrolyte was injected into the sealing plate,and a negative electrode was mounted on the separator. Thereafter, acase having an opening and a bottom, whose inner face (a round shapewith a diameter of about 12 mm) had been welded to another currentcollector plate, was mounted so as to cover the negative electrode, andthe opening edge of the case was crimped onto the gasket fitted to thecircumference of the sealing plate, to seal the case. As a result, acoin-shaped nickel metal-hydride storage battery S with a diameter ofabout 12.5 mm was completed. The height of the battery was about 2.25mm.

The batteries S were evaluated in the same manner as the batteries A. Asa result, it was found that the internal impedance was 0.9 Ω, thepositive electrode utilization rate at a discharge current of 6 mA was95%, and the discharge capacity at a discharge current of 30 mA was 25mAh.

EXAMPLE 18

Batteries T were produced in the same manner as in Example 1, exceptthat two parallel-connected positive electrodes and twoparallel-connected negative electrodes were used and that the depth ofthe case and the sealing plate was changed. In this example, a firstnegative electrode was mounted on the inner face of a+ sealing plate,and a first separator was mounted thereon. Subsequently, a firstpositive electrode was mounted on the first separator, and a secondseparator was mounted thereon. A second negative electrode was thenmounted onto the second separator, and a third separator was mountedthereon. A gasket was then fitted to the circumference of the sealingplate. Thereafter, an electrolyte was injected into the sealing plate,and a second positive electrode was mounted on the third separator.Thereafter, a case having an opening and a bottom, whose inner face (around shape with a diameter of about 12 mm) had been welded to a currentcollector plate, was mounted so as to cover the second positiveelectrode, and the opening edge of the case was crimped onto the gasketfitted to the circumference of the sealing plate, to seal the case. As aresult, a coin-shaped nickel metal-hydride storage battery T with adiameter of about 12.5 mm was completed. The height of the battery T wasabout 3.7 mm. The theoretical capacity of the positive electrode was 60mAh, which was the sum of those of the first positive electrode and thesecond positive electrode.

The batteries T were evaluated in the same manner as the batteries A. Asa result, it was found that the internal impedance was 0.6 Ω, thepositive electrode utilization rate at a discharge current of 6 mA was98%, and the discharge capacity at a discharge current of 30 mA was 54mAh.

Further, batteries U were produced in the same manner as in Example 18,except that a current collector plate was not welded to the inner bottomface of the case having an opening and a bottom, and they were evaluatedin the same manner. As a result, it was found that the internalimpedance of the batteries U was about 1.2 Ω, the positive electrodeutilization rate at a discharge current of 6 mA was 75%, and thedischarge capacity at a discharge current of 30 mA was 30 mAh.

Industrial Applicability

As described above, the present invention can suppress dimensionalchanges caused by the increase in battery internal pressure at the finalstage of charging and upon overcharge, and the degradation inelectrochemical characteristics due to uneven electrolyte distribution.Also, the present invention can reduce the contact resistance betweenthe electrode and the case or the sealing plate. Further, the presentinvention can provide an alkaline storage battery having excellentelectrochemical characteristics and low internal resistance at lowmanufacturing costs.

1. An alkaline storage battery comprising: (a) shallow case having anopening and a bottom; (b) a sealing plate covering the opening of saidcase; (c) a first electrode adjacent to an inner face of the bottom ofsaid case; (d) a second electrode adjacent to an inner face of saidsealing plate; (e) a separator interposed between said first electrodeand said second electrode; (f) an alkaline electrolyte; and (g) at leastone current collector plate selected from the group consisting of (g1) aconductive current collector plate joined to the inner face of thebottom of said case and forming a path distributed two-dimensionallybetween the inner face of the bottom of said case and said firstelectrode for allowing a generated gas to transfer and (g2) a conductivecurrent collector plate joined to the inner face of said sealing plateand forming a path distributed two-dimensionally between the inner faceof said sealing plate and said second electrode for allowing a generatedgas to transfer.
 2. The alkaline storage battery in accordance withclaim 1, wherein said path is distributed in an area of 50 to 100% ofthe whole inner face of the bottom of said case or the whole inner faceof said sealing plate.
 3. The alkaline storage battery in accordancewith claim 1, wherein said first electrode is 100 μm or more distantfrom the inner face of the bottom of said case, or said second electrodeis 100 μm or more distant from the inner face of said sealing plate. 4.The alkaline storage battery in accordance with claim 1, wherein one ofsaid first electrode and said second electrode is a negative electrodehaving a core material comprising punched metal.
 5. The alkaline storagebattery in accordance with claim 1, wherein one of said first electrodeand said second electrode is a negative electrode comprising a hydrogenstorage alloy or zinc.
 6. The alkaline storage battery in accordancewith claim 1, wherein said current collector plate (g) comprises aconductive porous material having pores that communicate with oneanother.
 7. The alkaline storage battery in accordance with claim 1,wherein said current collector plate (g) comprises a conductive sheethaving a plurality of protrusions.
 8. The alkaline storage battery inaccordance with claim 7, wherein said current collector plate (g)including said protrusions has an apparent thickness of 100 μm or more.9. The alkaline storage battery in accordance with claim 7, wherein saidcurrent collector plate (g) including said protrusions has an apparentthickness that is ⅓ or less of the thickness of said first electrode orsaid second electrode adjacent to said current collector plate.
 10. Thealkaline storage battery in accordance with claim 7, wherein saidplurality of protrusions have tip ends that are buried in said firstelectrode or said second electrode.
 11. The alkaline storage battery inaccordance with claim 10, wherein said tip ends buried in said firstelectrode or said second electrode have a length that is 10% or more ofthe apparent thickness of said current collector plate (g) includingsaid protrusions.
 12. The alkaline storage battery in accordance withclaim 7, wherein said conductive sheet having the plurality ofprotrusions comprises a metal sheet deformed by punching from one sideor both sides and has a plurality of pores and burrs formed around saidpores, and said conductive sheet including said burrs has an apparentthickness that is equal to or more than twice the material thickness ofsaid metal sheet.
 13. The alkaline storage battery in accordance withclaim 12, wherein pores closest to each other are formed by punchingfrom opposite sides, and burrs formed around said pores protrude inmutually opposing directions.
 14. The alkaline storage battery inaccordance with claim 12, wherein pores closest to each other have acenter-to-center distance of 0.3 mm or more and 5 mm or less.
 15. Thealkaline storage battery in accordance with claim 12, wherein said metalsheet before being deformed by punching has projections and depressions.16. An alkaline storage battery comprising: (a) a shallow case having anopening and a bottom; (b) a sealing plate covering the opening of saidcase; (c) a first electrode adjacent to an inner face of the bottom ofsaid case; (d) a second electrode adjacent to an inner face of saidsealing plate; (e) a separator interposed between said first electrodeand said second electrode; (f) an alkaline electrolyte; and (g1) atleast one spacer joined to the inner face of the bottom of said case andhaving at least one protrusion that forms a path distributedtwo-dimensionally between the inner face of the bottom of said case andsaid first electrode for allowing a generated gas to transfer, and/or(g2) at least one spacer joined to the inner face of said sealing plateand having at least one protrusion that forms a path distributedtwo-dimensionally between the inner face of said sealing plate and saidsecond electrode for allowing a generated gas to transfer.
 17. Analkaline storage battery comprising: (a) a shallow case having anopening and a bottom; (b) a sealing plate covering the opening of saidcase; (c) a first electrode adjacent to an inner face of the bottom ofsaid case; (d) a second electrode adjacent to an inner face of saidsealing plate; (e) a separator interposed between said first electrodeand said second electrode; (f) an alkaline electrolyte; and (g) at leastone current collector plate selected from the group consisting of (g1) aconductive current collector plate joined to the inner face of thebottom of said case and forming a gap between the inner face of thebottom of said case and said first electrode and (g2) a conductivecurrent collector plate joined to the inner face of said sealing plateand forming a gap between the inner face of said sealing plate and saidsecond electrode.